Compared to conventional silicon wafers, SOI wafers are superior in that separation between elements, a reduction in parasitic capacitance between an element and a substrate, and a three-dimensional structure are all possible, and they are consequently used in high-speed, low power consumption LSI.
One method for producing an SOI wafer is a Smart Cut method in which hydrogen ions are implanted in the silicon wafer surface and then cleaving heat processing is performed with the result that cleaving can be performed using the ion implantation layer as a boundary. However, as a result of damage caused by the cleaving, the surface of the SOI wafer after the cleaving (i.e., the cleaving surface) ends up as a rough surface. In order to solve this problem, for example, the SOI wafer production method described in Patent Document 1 discloses smoothing processing that employs a vapor etching method.
In addition, for example, in the SOI wafer production method described in Patent Document 2 a technique is disclosed in which the surface of the wafer after cleaving undergoes oxidization processing and is then heat-processed in a reducing atmosphere containing hydrogen so that the surface is smoothed.
However, in the mechanical processing method described in Patent Document 1, the amount of polishing layer is non-uniform, and it is difficult to obtain a uniform film thickness distribution in the SOI layer. Because of this, the technique to smooth using high temperature heat processing such as is described in Patent Document 2 is used. However, in the method of manufacturing an SOI wafer described in Patent Document 2, if smoothing processing is performed using a hydrogen gas etching effect, then etching irregularities tend to occur. These etching irregularities cause the film thickness of the SOI layer to not be uniform. Moreover, because safety devices are required due to the use of hydrogen gas, the resulting equipment costs are high which creates problems from a financial standpoint.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication, (JP-A) No. H11-102848
[Patent Document 2] Japanese Unexamined Patent Application, First Publication, (JP-A) No. 2000-124092